1. Field of the Invention
This invention relates to an apparatus for subjecting the inner wall of a tubular member to pickling treatment, and more particularly, to an apparatus for subjecting the inner walls of a wide variety of metallic tubes led by zircaloy tubes as cladding tubes for nuclear fuel to pickling treatment.
2. Description of the Prior Art
It has been known to pickle the inner walls of various metallic tubes, represented by stainless steel tubes. Depending on materials forming such tubular member, certain tubular member are pickled one by one using home industrial methods. In the case of stainless steel tubes, it is of course possible to immerse several tubes together in an acidic solution and to subject both outer and inner walls thereof to a pickling treatment. However, where tubes are made of, for example, zirconium or a zirconium alloy, it is improper or difficult to conduct the above-described dipping treatment. Thus, subsequent to the final annealing of these zirconium or zirconium alloy tubes, only the outer surfaces are polished to a roughness factor, for example, of about 6 s or so. Then, their inner and outer surfaces are pickled using an acidic solution such as nitric acid, fluoric acid or the like so as to obtain mirror-finished final products. Accordingly, if such pipes are brought into standstill or mutual contact during their pickling operation, there is a danger that pits, dents, or other surface irregularities would be developed on the surfaces thereof. Following pickling operation, it is necessary to immediately dip the tubular members into a neutralizing solution. If the residence time of the tubular members in the neutralizing solution is too long, irregularities tend to occur on the surfaces of the tubular members. Since the thickness reduction of a tubular member by pickling treatment is generally designed to be on the order of about 20.mu. at the outer diameter thereof, it is generally impossible to pickle several tubular members at once in order to follow the above-described standard. Furthermore, even in the pickling step per se, the treatment time period is strictly specified where the pickling treatment is carried out in two steps using both strong acid and mild acid. Moreover, it is necessary to continuously treat the thus-pickled tubular members to the water-rinsing step. Unless these steps are carried out in a manner even slightly different from that specified, there is a potential danger that white spots develope during the final test in an autoclave. This final test is generally conducted by users of the tubular members. Thus, unless such tubular members are carefully finished before their shipping to users, serious claims would arise from such users with respect to the quality of the tubular members. For the reasons mentioned above, it has heretofore been necessary to treat such tubular members one by one.
In order to solve various problems as described above, the present assignee has proposed in the past pickling apparatus exclusively for the inner walls of tubular members as disclosed in Japanese Patent Publication No. 15809/1978 (now, Japanese Patent No. 955215) and Japanese Patent Laid-open No. 123565/1978, which are incorporated herein as references. Satisfactory results have been obtained through the use of such pickling apparatus. As a result of extensive research carried out by the present inventors, it has been found that the commercial utility of such apparatus would be further improved by the provision of a mechanism to adjust the thickness so as to be reduced through the pickling treatment. Thus, the present inventors have ingeneously conceived of the concept of incorporating in such apparatus an instrument for measuring the inner diameter of a tubular member while subjecting the same to pickling treatment.
An ultrasonic wave (i.e., probe sensor) may be used as such an instrument for the determination of the inner diameter of a tubular member. However, the present inventors have realized that, where the general ultrasonic inner diameter measurement technology which is applied in air is employed as is, serious problems would arise because of: (a) the heat to be developed by the chemical reaction between the acidic solution and the tubular material; (b) special working conditions, in other words, the measurement and control of the extent of pickling must be carried out while proceeding with pickling treatment; (c) the inner diameter of a tubular member tends to vary at certain points along the length of the tubular member; (d) correction of the inner diameter may not be carried out smoothly--the inner diameter varies, for example, of the order of as much as 5 .mu.m along its length by a pickling operation of only 30 minutes: (e) when a plurality of tubular members are treated in lines or in series one time, the measurement values tend to become inaccurate.